Taking the bus or walking or cycling to work is linked with a healthier bodyweight, a study has found, leading experts to say government policy should focus on reducing use of the car.

The effect on bodyweight was greater than that seen after diet and exercise programmes, the scientists said.

Researchers found that men who took public transport or walked or cycled to work had a body mass index on average one point lower than those who used a car, the equivalent of half a stone in weight for the average man.

For women the effect was similar but less marked, with just less than one BMI point, the equivalent to 5.5lbs in weight.

Measurements of their body fat percentage mirrored BMI with those who used the car having higher body fat.

The researchers from the London School of Hygiene and Tropical Medicine and University College London, said the findings were robust and showed that the health benefits of taking public transport were boradly similar to walking or cycling.

Lead author Ellen Flint a research fellow at the Department of Social and Environmental Health Research, at London School of Hygiene and Tropical Medicine wrote in the British Medical Journal online: "A key finding from this study is that the effects observed for public transport were very similar in size and significance to those for walking or cycling to work.

"This finding may have important implications for transport and health policy, as over the past decade the proportion of commuters who walk or cycle to work has remained stubbornly low outside major cities in the UK.

"Greater emphasis on encouraging a shift from private to public transport modes may plausibly have significant population health benefit and may be more acceptable to commuters.

"Such a strategy could also yield large environmental benefits, and could be an important structural intervention to combat obesity."

She added that the size of the effect was 'clinically meaningful'. She said: "These differences are larger than the effect sizes seen in most individually focused interventions based on diet and physical activity to prevent overweight and obesity."

She concluded: "Given that most commuters in the UK use private transport as their main mode, there are potentially large population-level health gains to be made by shifting to more active modes of travel.

"The use of public transport and walking and cycling in the journey to and from work should be considered as part of strategies to reduce the burden of obesity and related health conditions."

The study took BMI measurements, which is weight divided by height squared, and body fat measurements from 7,534 men and women. Their average BMI was 28 for men and 27 for women, classed as 'overweight'.

Men who commuted via public or active modes had BMI scores around 1 point lower than those who used private transport, equating to a difference in weight of 3kg (almost half a stone) for the average man.

Women who commuted via public or active transport had BMI scores around 0.7 points lower than their private transport using counterparts, equating to a difference in weight of 2.5kg (5.5lb) for the average woman.

The results took into account differences in age, illnesses or disability, income, diet and whether they took part in sport among other things.

In an accompanying editorial, researchers from Imperial College London said the reason why the effect of the use of public transport was as great as walking or cycling was probably because it involves walking or cycling to bus stops or train stations and this increases 'incidental activity'.

Anthony Lavery and Christopher Millett wrote: "Consistent with this is the finding that provision of free bus travel to older people in England has been associated with greater use of public transport, more frequent walking, and a lower likelihood of becoming obese."

They added that two thirds of people now drive to work, up from less than half in 1970.

They said discouraging car use was 'politically sensitive' and doctors should reiterate the message instead.

"Healthcare professionals are additionally well placed to advise patients to “leave your car at home” and increase the number of trips they make for work, shopping, and leisure using public transport, walking, or cycling.

"This will not only improve their patients’ health in the short term but also help reduce the likelihood of hazardous climate change further in the future," they wrote.